Redis uses Tcmalloc to cause memory not to be freed

From:http://wangneng-168.iteye.com/blog/2100379

Redis uses tcmalloc to manage memory, and when a Redis key is removed, the redis Info command is used to view memory usage. The memory is not released, but the default jemalloc does not have this problem

The following is the memory condition that is seen through info after deleting the key after using Tcmalloc and deleting key:

Delete key Before:

used_memory:13051400

used_memory_human:12.45m

used_memory_rss:16326656

used_memory_peak:13051400

used_memory_peak_human:12.45m

used_memory_lua:33792

mem_fragmentation_ratio:1.25

mem_allocator:tcmalloc-2.0

Delete key after

used_memory:835080

used_memory_human:815.51k

used_memory_rss:16392192

used_memory_peak:13051400

used_memory_peak_human:12.45m

used_memory_lua:33792

mem_fragmentation_ratio:19.63

mem_allocator:tcmalloc-2.0

The following is the memory condition that is seen through info after deleting the key after using Jemalloc and deleting key:

Delete key Before:

used_memory:13047176

used_memory_human:12.44m

used_memory_rss:14704640

used_memory_peak:13047176

used_memory_peak_human:12.44m

used_memory_lua:33792

mem_fragmentation_ratio:1.13

mem_allocator:jemalloc-3.6.0

Delete key after

used_memory:830696

used_memory_human:811.23k

used_memory_rss:2318336

used_memory_peak:13047176

used_memory_peak_human:12.44m

used_memory_lua:33792

mem_fragmentation_ratio:2.79

mem_allocator:jemalloc-3.6.0

from the results, after deleting a large number of keys, Redis allocated memory with Jemalloc reduced to about 2M, while Tcmalloc did not change

Tcmalloc the principle of:

Http://wenku.baidu.com/link?url=pzXI4OTNuoNGPKQ9MtKOX_ 60adnrekve5m94qnuzmj0bsgcaxodpcvolchwd4bjagaqbsrnn2acxzne9mp4fshzm2a-oxt02ohmbyrhcblw

It is mentioned that the current Tcmalloc version does not return any memory to the operating system, and the memory occupied by Redis instances when using Tcmalloc is related to the peak memory usage of Redis

JeMalloc the principle can be see:

http://club.alibabatech.org/article_detail.htm?articleId=36

which mentions:

The recycling process is broadly similar to the distribution process, withTcacheWill cache the collected blocks withoutTcacheDirect recovery of the mechanism (no more thanChunkthat will correspond to thepageThe state is modified to reclaim the correspondingRun; greater thanChunkthe directMunmap). It is necessary to focus onJemallocwhen will the memory be returned to the operating system becausePtmallocexists because of the use ofTop_chunkmechanism (see the articles in the court) and make the memory unavailable to the operating system. At present, except for the large memory directlyMunmap,JemallocThere are also two mechanisms to free up memory:

1. when released , it is found that all the memory of a chunk is dirty (i.e., after being allocated and recycled), the entire chunk is released;

2.whenArenain thepagewhen the allocation satisfies a thresholdDirty PagemakePurge(by callingmadviseto proceed). The specific meaning of this threshold is that theArenain theDirty Pagesize has reached aChunksize and account for theactive Pageof the1/opt_lg_dirty_mult(the default is1/32). active PageIt means that it is already in use.Runof thepage, whileDirty Pageis the one that has been allocated and recycled.page.

Both of these mechanisms ensure that jemalloc does not appear to have issues like ptmalloc memory not being returned to the operating system

Conclusion: It is good to use Tcmalloc and jemalloc with caution.

Redis uses Tcmalloc to cause memory not to be freed